The present invention relates to a process for producing bisphenol A in which the life of the acid-type ion-exchange resin used as a catalyst can be prolonged.
Bisphenol A [that is, 2,2-bis (4-hydroxyphenyl)propane] is an important starting compound for engineering plastics such as polycarbonate resins, polyarylate resins and others and for epoxy resins, etc. There is increasing the demand for bisphenol A with the increase in the production of such resins.
It is known that bisphenol A is produced by reacting acetone with excess of phenol in the presence of an acid-type ion-exchange resin catalyst and a sulfur compound promoter such as alkylmercaptans, etc. In this reaction, the acid-type ion-exchange resin catalyst used degrades time-dependently. The primary reason for it will be heavy substances derived from acetone. The degradation of the catalyst starts around the inlet of the reactor. Since the degradation speed is high, excess of the catalyst shall be filled into the reactor to ensure long-run continuous operation. In order to keep the intended output of bisphenol A being produced (that is, in order to keep the conversion of phenol being reacted) even after the catalyst used has degraded, acetone to be fed into the reactor must be increased time-dependently. Since the non-reacted acetone must be recovered from the reaction mixture through distillation, the amount of acetone to be increased shall be limited depending on the capability of the distillation unit used. In other words, the catalyst must be exchanged for a fresh one when the capability of the distillation unit has reached its limit. Accordingly, properly controlling the reaction condition so as to prolong as much as possible the life of the catalyst being used could reduce the frequency of catalyst exchange, thereby reducing the production costs. In this connection, methods of using a plurality of reactors to control the reaction condition are proposed in Japanese Patent Laid-Open Nos. 19952/1979 and 17144/1990.
In the method proposed in Japanese Patent Laid-Open No. 19952/1979, two or more reactors are disposed in series, and a carbonyl compound, divided into plural portions, is added to each reactor whereby the concentration of the bisphenol product in the fluid from the latter reaction zone is substantially increased with no negative influences on the properties of the ion-exchange resin catalyst used and the properties of the phenol recovered. However, in the method concretely illustrated therein, a single reactor is used, and nothing is disclosed therein that relates to the high-level phenol conversion attained by the present invention.
The method proposed in Japanese Patent Laid-Open No. 17144/1990 comprises adding an alkylmercaptan, divided in plural portions, to a series of reactors to thereby inhibit the formation of cyclic diner by-products. In the method disclosed therein, used is two reactors for producing bisphenol A. However, in the method disclosed, used is a large amount of methylmercaptan that reaches 50% by weight of the reaction product. In this, therefore, there is little possibility of increased phenol conversion, and the life of the catalyst used could not be prolonged so much.
In the situation as above, the present invention is to provide a method of producing bisphenol A in which the life of the acid-type ion-exchange catalyst used can be prolonged.
We, the present inventor have assiduously studied the outstanding problems in the art, and have found that, when three or more reactors connected in series are used in such a manner that all of phenol, all of an alkylmercaptan and a part of acetone are fed into the first reactor while the remaining acetone, divided into plural portions, is into all the second to the last reactors, then an increased phenol conversion can be ensured. On the basis of this finding, we have completed the present invention.
Specifically, the invention is to provide a method of producing bisphenol A by reacting phenol and acetone in the presence of an acid-type ion-exchange resin serving as a catalyst and an alkylmercaptan serving as a promoter, in which three or more reactors connected in series are used and all of phenol, all of an alkylmercaptan and a part of acetone are fed into the first reactor while the remaining acetone, divided into plural portions, is into all the second to the last reactors to produce bisphenol A.